Designing and Characterizing a Truly Green Composite from Bio-based Polymers and Fillers

As commodity polymers and plastics continue to be produced from petroleum-based resources and contribute to negative environmental effects, we developed a renewable alternative to traditional composites through the use of biologically based precursors.Epoxidized soybean oil (ESO) has the potential to be cured into an epoxy-like thermoset polymer. Because of inferior mechanical properties compared to petroleum-based counterparts, ESO was blended with equal part traditional epoxy. SuperSap ONF, a commercial hardener, was identified as an appropriate hardener, which yielded an ESO-traditional epoxy blend that is 44% bio-based. This bioepoxy was weaker and less stiff, but 35% more bio-based, than a commercially-available, bio-based SuperSap ONE.Unidirectional flax composites were created with our formulated bioepoxy and commercial FlaxTape 200, at a fiber loading of 29%, via vacuum assisted resin transfer molding (VARTM). These composites were then mechanically (tensile, flexural, dynamic mechanical analysis, and Izod impact) tested parallel (0°) and perpendicular (90°) to loading and compared to two well-established composite models: the rule of mixtures (ROM) and the inverse rule of mixtures (IROM).The modulus of 0° composite samples was 24 times greater than the neat bioepoxy. The strength (defined by maximum stress) of the composites in both tensile and flexural tests was not nearly as high as those predicted from the associated rule of mixtures models. Impact testing found parallel loaded samples to be four times more resistant to impact than the neat bioepoxy. Flax did not impact the glass transition temperature of the bioepoxy (48°C). The formulated composite was 60% bio-based.